1. Technical Field
The present invention relates to nonvolatile storage devices, integrated circuit devices, electronic apparatuses, and the like.
2. Related Art
A nonvolatile storage device can hold memory without being supplied with power and is used in various electronic apparatuses. Here, an electronic apparatus installed in an automobile or the like that requires safety requires high reliability. In such an electronic apparatus, a nonvolatile storage device also requires high data reliability.
For example, the inventions of JP-A-2002-358794 (hereinafter Patent Document 1) and JP-A-2005-92962 (hereinafter Patent Document 2) include a redundant memory cell which is used in place of a memory cell that has developed a defect and thereby increase data reliability. Patent Document 1 proposes a technique of speeding up the read speed by reducing the wiring load when the redundant memory cell is used and Patent Document 2 proposes a technique that makes it possible to perform accurate and stable reading by providing a read path separately when the redundant memory cell is used.
In recent years, a high-capacity (for example, a few gigabit) nonvolatile storage device such as flash memory can be used. At this time, as in the inventions of Patent Document 1 and Patent Document 2, providing a redundant memory cell is suitable as a method for increasing reliability.
On the other hand, there is demand for low-capacity and inexpensive OTP (one time programmable) memory for performing, for example, calibration of analog circuits in which variations can occur depending on products. The OTP memory is nonvolatile memory that allows writing only once. For example, FAMOS (floating gate avalanche-injection MOS) is a type of nonvolatile memory and allows written information to be deleted by ultraviolet rays. However, the FAMOS can be used as low-capacity OTP memory after being covered with a commonly-used IC package with no window for ultraviolet irradiation.
In such uses, FAMOS of tens of bits, for example, is sometimes used. At this time, providing a redundant memory cell results in an increase in circuit area at a large ratio thereof to the whole portion and is not practical for a method for increasing reliability.
Therefore, as a method for increasing the reliability of low-capacity and inexpensive OTP memory, to perform satisfactory analysis in the event of a breakdown, it is necessary to reduce the number of places that cannot be tested.